implacable

He imagined that some secret society, some implacable organization, was on Douglas’s track, which would never rest until it killed him.

He renewed against Danglars, Fernand, and Villefort the oath of implacable vengeance he had made in his dungeon.

“Implacable resentment _is_ a shade in a character.

When Franz had finished reading this account, so dreadful for a son; when Valentine, pale with emotion, had wiped away a tear; when Villefort, trembling, and crouched in a corner, had endeavored to lessen the storm by supplicating glances at the implacable old man,—